1. Department of Astronomy, Beijing Normal University, Beijing 100875;2. National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101;3. School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049;
Kepler 卫星提供的长时序、高精度的光度观测和郭守敬望远镜(LAMOST)提供的大规模光谱观测为研究恒星表面转动周期与富锂巨星锂丰度关系提供了良好的数据. 将LAMOST搜寻到的富锂巨星与Kepler 观测交叉, 获得了619颗共同源, 研究了其 中295颗有良好观测数据的富锂巨星的表面转动. 在205颗有星震学参数的恒星中提取出14颗恒星的转动周期, 其中氦核燃烧星(HeB) 11颗, 红巨星支(RGB) 2颗, 1颗演化阶段未确定. 本样本中的极富锂巨星(A(Li) > 3:3 dex)皆为HeB; 对于90颗没有星震学参数的样本因而没有依靠星震学手段确定演化阶段的恒星中, 有22颗提取出了自转周期. 前者的自转探测率为6.8%, 显著高于之前工作中大样本巨星2.08%的探测率. 同时, 此研究首次从自转周期的角度确认了恒星转动与巨星锂增丰存在相关性, 在增丰程度较弱时, 自转周期分布比较弥散; 强锂增丰的星倾向于快速转动. 富锂巨星与极富锂巨星在转动速度随锂丰度的演化上展现了两个序列, 在转动-锂丰度图上的A(Li) 3:3 dex处产生第2个下降序列, 或许暗示了两者在形成机制上的不同. 极富锂巨星的样本中, 随巨星锂增丰程度增强, 恒星转速加快. 这种相关性为由转动引起的额外混合作为富锂巨星形成的机制提供了支持.
The years-long and high-precision photometric data observed by Kepler satellite combining with huge amount spectra observed by LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope) provide a great opportunity to study the relations between surface rotation and lithium abundance of Li-rich giants. In this study, we cross match the Kepler data with Li-rich giants catalog from LAMOST, and obtain 619 common sources. Then we measure 36 rotation periods from the full set of 295 Li-rich giants with good data quality which consists of two sub-samples. The rotation periods of 14 stars were extracted from 205 stars with evolutionary stages determined using asteroseismology, including 11 core helium-burning stars (HeBs), 2 red giant branch stars (RGBs), and 1 unclassified star. All the super lithium-rich giant stars (A(Li) > 3:3 dex) are HeB in our sample. The remaining 90 giants do not have evolutionary stages confirmed, and in this sub-sample, 22 giants have their rotation period measured. The rotation detection rate of the former sub-sample is 6.8%, which is significantly higher than the detection rate of a large giant sample in previous studies (2.08%). With surface rotation period measured, we confirm the relation between stellar rotation and lithium enrichment of giants. Meanwhile, we find that the less Li-enriched stars have a relatively dispersed rotation period, and giants with high Li enrichment concentrate on the rapidly rotating area, which are consistent with earlier studies. The present work also shows a jump at A(Li) 3:3 dex in the relation between rotation period and Li abundance that coincidently is the boundary between Li-rich giants and super Li-rich giants, which may indicate different mechanisms. The rotation periods of super Li-rich giants become shorter as the lithium enrichment increases.This correlation provides evidence for the rotationally induced extra-mixing mechanism responsible for Li enrichment of giants.